


Good Boy

by Illuminaughtysins



Category: Undertale (Video Game)
Genre: Daddy Kink, Dirty Talk, Double Penetration, Ecto-Genitalia, Incest, M/M, Multi, Oral Sex, Orgasm Delay/Denial, Plot What Plot/Porn Without Plot
Language: English
Status: Completed
Published: 2016-06-05
Updated: 2016-06-05
Packaged: 2018-07-12 11:31:27
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,405
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7101451
Author URL: https://archiveofourown.org/users/Illuminaughtysins/pseuds/Illuminaughtysins
Summary: <blockquote class="userstuff">
              <p>Gaster returns home late to find the boys .. occupied. That just won't do.</p>
            </blockquote>





	Good Boy

**Author's Note:**

> Inspired by artwork by Spoopy-gaster over at tumblr. Check out their stuff!
> 
> This is the.. third fanfic I've ever written, second for Undertale, and first that I've been brave enough to post up here on AO3. Unbeta'd, so all mistakes are mine, crossposted to my tumblr where I have the same username. 
> 
> Bury me in an unmarked grave.

 

It wasn’t unusual for him to come home late in the evenings. His work at the lab required a great amount of time spent pouring over his own research, checking and rechecking over and over. He had to be careful; the possibilities of something going _wrong_ were near astronomical. Gaster was fairly certain he even worked out the exact number for those odds, once. It was probably buried in a stack of paper somewhere.

When he did return late into the evening, it was fairly typical what he would be find: Sans and Papyrus having gone to bed, occasionally the two of them snoozing on the couch or fighting sleep to meet him before they succumbed to the need to rest. Sans usually covered the ‘nap’ part, while Papyrus would cover the duty of attempting to stay awake, always proud when he managed it and could greet the doctor with a wide smile.

Tonight they were both.. awake. Very awake.

Papyrus sat upright on the couch, Sans sprawled partially in his lap. The taller skeleton had him supported with one arm to keep him upright, their skulls pressed together. His other hand was down the others’ shorts, ever so slight movement noticeable to Gasters careful eyes.

Sans had his eyes closed, too wrapped up in what his brother was doing to him to even realize the doctor had stepped through the door. Papyrus, however, met his eyes over the top of his skull, a knowing glint there.

Gaster let a slow smile make its way onto his face. That look had meaning, and he knew it well. Usually it was Papyrus himself between the other two monsters, but every now and then he seemed to have the urge to see his brother fall apart. It seemed he was in a mood. As if to extend that point, he made a quick move with the hand he had down Sans’ shorts, the smaller monster letting out a cry.

The doctor knew how to walk silently, move without being seen—but it was hardly necessary, Sans far too distracted to even look up from where he had buried his head in his brothers scarf, panting in small, quick bursts. Standing a few feet away but still able to meet Papyrus’ eyes, Gaster made a few quick signs with his hands to tell the other monster what he wanted. He couldn’t help his crooked smile when his request made the tall skeleton shudder.

Withdrawing his hand from where it had been buried within his brothers shorts, Papyrus showed off his blue-tinted glove, tsking quietly.

“Really, Sans. You make such a mess!”

Sans only groaned, the sound somewhere between frustrated and relieved. The former for a small, much needed break, the latter because he didn’t really _want_ a break from his brothers attentions. Before he could take stock of anything, Papyrus shifted him how Gaster had silently requested, pulling the smaller skeleton into his lap proper with his knees resting on the couch cushion just outside of the taller skeletons. It was an open position, and he readjusted the arm he’d been supporting his brother with to push his back into an arch to make it that much more so.

“There. That’s better, I think,” Papyrus murmured, urging Sans’ arms up to wrap around his neck for support.

“y-yeah.. c’mon, pap. don’t leave me hangin’, here,” Sans groaned, shifting restlessly in the others lap.

“I won’t,” the taller skeleton soothed, reaching with his soiled glove to push his brothers shorts down off his hipbones. Gaster bit down on two of his fingers to keep from making any noise just yet, eyes fixed on the absolute mess that had been revealed. Papyrus must have been in _quite_ a mood to talk Sans into conjuring the pussy that lay between his legs, even more so to have apparently been fingering him for stars only knew how long.

Licking at his teeth, Gaster nodded to Papyrus as he drew closer. The taller skeleton tightened the hold he had on his brother, slowly spreading his legs and, in turn, Sans’. He stopped when the smaller monster groaned, reaching up with the hand he’d used previously and spreading the slick folds even wider with his fingers.

“Want something, Sans?”

“ooh.. come on, pap. have a heart, i’m.. i’m practically gushing here.”

“ _We noticed,”_ Gaster drawled, kneeling behind Sans and placing his hands on his hips to keep him from moving all in one fluid motion.

“wh-! g-gaster?! when di—ah!”

His startled surprise was interrupted as the doctor leaned forward, licking a quick line up his soaking folds before pushing his conjured tongue down into him properly. Sans held onto his brother like a lifeline while he shuddered. Gaster hummed and released one side of his hip to press two fingers in alongside his tongue. He thrust them at a slow but firm pace, the skeleton above him muffling his sounds in his brothers shoulder.

“ah, hh.. f-fuck,” Sans rasped, mouth falling open and showing the blue tongue that lay within. Papyrus moved one hand up, soothing at the back of his brothers skull.

“I think he likes that..”

Gaster withdrew his tongue as he chuckled, rubbing firmly with his fingers before he removed them as well. He licked at the fluid that covered them and spoke in a low, pleased tone.

“ _Yes… What a good boy you are, Sans… Taking all of daddy’s tongue inside you…_ ”

The small skeleton groaned and shuddered as he gave his head a small shake.

“please, i’m so… i need to—“

Kneeling up straighter, Gaster ran his hands up the small skeletons frame, gently pulling him upright and away from where he had been leaning into his brother.

“ _Now, now. That’s a bit selfish, isn’t it? What about your brother?”_

He let his head rest upon Sans’ shoulder, nodding his chin towards Papyrus. An orange flush was present upon the taller skeleton and his hands fidgeted upon the couch cushion now that he wasn’t holding his brother. Clearly, he wasn’t unaffected by all that had been going on.

“ _Seems a bit one sided, don’t you think? Why don’t you help him while I see what I can do for you.”_

Sans groaned and shuddered against him but nodded. The doctor smiled and nodded to Papyrus as he pulled the smaller skeleton down off the couch to kneel on the floor between them, the younger of the two shifting to remove the clothes that lay in the way. He let out a relieved breath when he could properly let his magic form, his length a deep shade of orange.

“ _Go on. He deserves it after all he did for you, doesn’t he?”_

Distracted and clearly foggy-minded, Sans leaned forward to wrap one hand around the base of the cock his brother has conjured while dipping his head down to lave his tongue across the head. Papyrus gasped above him, hands moving uselessly before he lay them on his brothers head. Not pushing or moving, just holding there for something to ground himself.

“ _Good boy,_ ” Gaster praised, one hand returning to the small skeletons wet folds while the other began to pull at his own clothing. He thrust in two fingers with little warning, pulling a muffled shout out of Sans and resulting in a quiet whine from Papyrus in turn. The doctor smiled, pushing his fingers in and out with a slow pace that was sure to keep the other skeleton riled but away from his peak. Sans groaned as he began to bob his head, eyes unfocused as he let himself get lost between the two.

Spreading his fingers as he continued the slow press in and out, Gaster kept a careful eye on the skeleton he was teasing. If this was to go as he planned, he’d have to watch for the signs that Sans was close. He quickened his pace, earning a quiet, muffled whine. Keeping it up, he waited until Sans was starting to shift restlessly and tightening around his fingers before stopping the movement completely, fingers still buried but unmoving.

Sans whimpered below him, trying to shift or do anything to get him to move, but was held in place as he was between the two. Free from the clothing in his way, Gaster let out a pleased hum and removed his fingers. Stars, but they were **drenched**. He knew he could keep Sans right on the edge if he was careful, but it would take patience.

“ _Easy,_ ” he soothed, running a hand up along his spine over the jacket he still wore. Sans slowly calmed with increments until he seemed more grounded. “ _There you go.”_

He grasped at his own length to steady it before running the head of it up the slick folds and pressing forward. In front of him, Sans pulled off of his brothers cock with a wet gasp, head dropping down as he shuddered. Orange-tinted precum smeared across his cheekbone and his hand kept stroking but for the moment all he could do was pant and moan, overwhelmed as the doctor slowly hilted himself.

“ _Stars, y-you’re so tight. Such a good boy for me,”_ he whispered, continuing his soothing touch up and down his back. “ _Try and focus.”_

With a low groan Sans lifted his head once again and took the cock in front of him into his mouth, tongue wrapping around it as he set back into the rhythm he’d had before. Papyrus shuddered, fingers digging in to where he still held at his head. The doctor chuckled and began to move at a horribly _slow_ pace that was sure to be pleasurable but not nearly stimulating enough.

Papyrus groaned, hands shifting restlessly at where they held. Gaster may be sticking to a teasing pace, but Sans hadn’t. As if to spite the slow thrusts, he ducked his head down low to take in as much of his brothers length as he could and speeding up how fast his tongue moved over it. He _needed_ the distraction the act provided; Gasters thrusts were going to drive him mad if he didn’t. He was so close but his climax was being kept just out of reach.

“H-hha, Sans—ah!”

Whatever he’d been about to say vanished from his mind as Sans moved back up, tongue licking around the head of his cock to gather up the precum that had collected before diving his head back down.

“ _Ch **eek** y **li** ~~ttl~~ e ~~**thing**~~ ,”_ Gaster hummed unevenly, voice dipping in and out of his wingding speech as he slowly began to pick up his pace. All the teasing he’d done had an effect on him just as much as it did Sans and holding back was beginning to be something of a challenge. “ _G **iv** e your b-br ~~othe~~ r what he n ** ~~eed~~** s and I’ll give **you** what you ~~wan~~ t.”_

Sans whimpered as he tried to speed up, desperation making him sloppy in his attempts. He seemed to give up, pulling up off Pap’s length with a wet gasp and looking up to his brother while he wrapped his fingers around his cock and began to quickly stroke.

“c-come on, paps. know you’ve been on edge just as long as i have, haven’t you?” He licked around the head once again, breath beginning to come in pants. “i want to feel it—want you to come on my face. you wanna do that, don’t you?”

“ _C ~~he **ate**~~ r,” _Gaster murmured, but it had worked. Papyrus’ gasp was cut off by his own whine as his hips jerked forward, using the hold he had on Sans to push him back just far enough so that his face sat directly in front of his cock as he came. The skeleton between them let his mouth fall open, groaning low as his brother’s release streaked across his face. Some of it managed to land on his tongue and he glanced over his shoulder to Gaster before swallowing, making a show of it.

“ _D ~~irty~~ b **o** y.”_ The doctor pulled him upward so his own chest was to his back, giving a harsh thrust that made the other skeleton cry out and scramble for something to hold on to. Papyrus was there in a second, leaning forward to give him something to cling to as Gaster moved to an almost punishing pace, clearly done teasing.

“ _S ~~uc~~ h a g **oo** d boy f ~~or~~ ~~me~~ ,” _he whispered, pulling Sans into each of his thrusts with an arm around his rib cage. The other went down to rub at his clit, making him shriek and clench down around his length. “ _Ngh-hha.. ~~Doin~~ g just what I ~~**ask**~~. So w ~~el~~ l beh ~~ **ave**~~ d.”_

“i ca-an’t, gaster, i, i—“

“ _Say what I w ~~an~~ t to h **ear** , p ** ~~retty~~** boy.”_

Sans panted, only held up by the hold both of the others had on him. “please, please daddy, i gotta—“

“ _ ** ~~Good~~** ,”_ he groaned, licking along the edge of his jaw and some of the orange-tinted cum that lay there as he ground his length as deep as he could. “ _C ** ~~ome~~** f ~~o~~ r m ~~ **e**~~.”_

Sans shouted as he clenched down, clinging to Papyrus’ shoulders as he shook with his orgasm. Gaster continued to thrust, prolonging the sensation as he chased after his own peak. It only took a few more jarring moves before he hilted himself and shouted an unintelligible mix of the smaller skeletons name and _yes_ in wingdings.

For a long few moments the only sound in the room was the slowly steadying breath of all three. Papyrus was the first to move as he raised his hands, one lifting his brothers the chin while the other soothed over the back of his head. Gaster was next, kneeling up straight and pulling out his length. He looked down to watch the mix of fluids drip down out of Sans’ conjured pussy, chuckling quietly and pressing a kiss to his shoulder.

“ _Beautiful,”_ he murmured, hands easing up and down his back to try and bring him back down from his overstimulated haze. Sans didn’t bother to reply, pants and gasps quieting as the two worked to calm him. “ _Papyrus, it looks like I may need your help.. I don’t think he’s walking anytime soon. Lets get the both of you cleaned up and to bed.”_


End file.
